The null and undefined should be added to false values

[jcubic]

Accord to Scheme spec #f should be the only falsy value, but LIPS use two constants from JavaScript : null and udefined. I was caught multiple times when using String::match when I didn't use: (not (null? x)).

This will simplify user code if both null and undefined are false values. So the old behavior will be restored.

It's kind of silly that null and undefined are true.

It's intuitive to write:

(if (str.match #/foo/)
    (display "it's foo"))

• Update if
• Update and
• Update or

[lassik]

Several Scheme implementations have an "unspecifed" or "void" value. It is returned by procedures where RnRS says the return value is unspecifed. JS undefined would be a good fit for this purpose.

The unspecified/void value is not considered false. This is intentional.

Survey

[lassik]

RnRS has no clear equivalent to JS null. Perhaps look at how Kawa handles Java's null.

[jcubic]

Thanks will check.

[jcubic]

Maybe I should add warning when if, and, or gets null or undefined as argument. Scheme forces to use #f as the only false value, but if users use if with null this is probably a mistake on his end. I can make a flag to disable the warnings. @lassik what you think about something like this.

[jcubic]

Kawa have #!null and #!void constants:

(unless #!null (display "x\n"))
;; ==> x
(when #!void (display "x\n"))
;; ==> x

so null is false in Kawa.

[lassik]

Maybe I should add warning when if, and, or gets null or undefined as argument.

That might be a good idea.

null is false in Kawa.

That probably makes sense, because null has a similar purpose in Java (and JavaScript) as #f has in Scheme. Both null and #f are used to indicate "it would be meaningful to have an object here, but we don't have one now". This is similar to nil in Lisp. (As you say, Scheme does not use nil.)

In Scheme, undefined and void indicate "it would be meaningless to have an object here".

[lassik]

For example, assoc returns #f to indicate "I tried to find an object, but I didn't find one".

But write returns unspecified because it would be meaningless to return anything.